The manifold biological effects of small peptides such as hormones and antibiotics warrant the study of the interactions of cells and peptides. We propose to study the structural and physiological requirements for the covalent attachment of peptides to components of the peptide transport system in microorganisms, predominantly Saccharomyces cerevisiae. Affinity labels and photoaffinity labels will be used to insert radioactive, chromogenic, and fluorescent markers into transport proteins to aid in their isolation and to study the microenvironment of integral membrane proteins. Peptides will be bound to soluble and insoluble macromolecules to probe the location of transport proteins in the cell envelope and to isolate transport components, using affinity chromatography. The dodecapeptide yeast mating factor, termed alpha-factor, will be synthesized and attached covalently to poly(ethylene glycol), a water soluble macromolecule. The conformation and biological activity of this peptide-polymer will be studied. Yeast plasma membrane vesicles will be used to examine the molecular interactions of the alpha-factor with its receptor. Procedures developed during attempts to isolate peptide transport proteins will be applied to isolation of the alpha-factor receptor. These studies should increase the understanding of membrane transport systems and receptors, in general, and may provide insights into the detailed manner by which peptide hormones are recognized and processed by mammalian cells.